There are items that increase maximum resistance but you can't get any higher than 95%. The guardian Angel armor ups all resists by 15%. Waterwalks boost max fire resists. And I think Venom Guard cranks up poison. I also think the unique ringmail boosts all resist maximums by 5%.

Also a Paladin gains a passive bonus to maximum resist by putting points into his three resist skills at 2 for 1 and it goes up to 1 for 1 for that specific aura any time he uses.

However, 75% is really good enough because you can use absorb items to make yourself pretty much immune to an element. Raven Frost rings, for instance, absorb 20% of all damage from Ice attacks meaning they reduce damage by 20% and heal it back instantly effectively covering 40%.